Today, the Trump administration is slapping tariffs on another $16 billion worth of imported goods from China. And China is expected to retaliate. Since taking office, Trump has used tariffs with the goal of protecting favored industries and punishing countries for unfair trading practices. As NPR's Jim Zarroli reports, he has taken tariffs further than any other modern president.

JIM ZARROLI, BYLINE: Trump has been a hard-liner on trade for a long time. Here he was back in 1988 on "Oprah."

(SOUNDBITE OF TV SHOW, "THE OPRAH WINFREY SHOW")

PRESIDENT DONALD TRUMP: I'd make our allies pay their fair share.

ZARROLI: He singled out Japan, saying its markets were closed to American companies.

(SOUNDBITE OF TV SHOW, "THE OPRAH WINFREY SHOW")

TRUMP: It's not free trade. If you ever to go to Japan right now and try to sell something, forget about it, Oprah. Just forget about it. It's almost impossible.

ZARROLI: Now that he's president, Trump is trying to put those beliefs into practice. Since taking office, Trump has often been hamstrung by Congress and the courts. But tariffs are one area where presidents can sometimes act unilaterally. And Trump has been more than willing to use them as a weapon. Brad Setser is a senior fellow at the Council on Foreign Relations.

BRAD SETSER: I do think that Trump is unique. He's unique in a lot of ways, but certainly, his willingness to use tariffs sort of on a whim feels very different.

ZARROLI: This year, Trump imposed tariffs on imports of steel and aluminum. He said they were necessary on national security grounds.

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TRUMP: We want to build our ships, we want to build our planes, we want to build our military equipment with steel, with aluminum from our country.

ZARROLI: He followed those up with big tariffs on Chinese imports. When China retaliated, he imposed even more. Economist Doug Irwin of Dartmouth College says other presidents have sometimes imposed tariffs after a specific industry complained that it was facing unfair competition from imports. President Reagan used tariffs against Japan to protect U.S. autos, for instance. But Irwin says the Trump administration has jumped in to protect companies even before being asked.

DOUG IRWIN: It seems to actually want these tariffs in many instances. They've pushed for cases themselves rather than waiting for private industry to file them, and then following through very quickly with high tariffs.

ZARROLI: More recently, Trump asked the Commerce Department to look into tariffs on European cars. It's a move opposed by U.S. automakers, who say it could wreak havoc on supply chains. And earlier this month, Trump imposed tariffs on Turkish steel not for any reason having to do with trade, but to punish the government for keeping an American minister under house arrest. And Brad Setser says that's unusual.

SETSER: What I think is a little bit new and different is to use trade policy in such a direct way in a foreign policy dispute.

ZARROLI: Trump has imposed tariffs more than any president in recent times, says Celeste Drake, trade specialist at the AFL-CIO. And she says that's not necessarily bad. Tariffs can be a good tool to force countries to the bargaining table. But Drake isn't confident there's a method behind Trump's policies.

CELESTE DRAKE: I think there are many questions about whether or not the tariffs are really targeted to the right players and being used strategically with clear goals in mind.

ZARROLI: She points to Trump's decision to impose steel and aluminum tariffs on close U.S. allies such as Canada. Trump has generally brushed aside such criticism. As a private citizen, Trump saw tariffs as a vital tool for protecting America's economic interests. Since taking office, he appears to have only grown firmer in those convictions. Jim Zarroli, NPR News, New York.